Nanoscale silicon particles have many current and potential commercial uses1, including electronics, sensors, high-hardness chemoabrasives3, optoelectronics4, optomagnetic switches5, electronic storage6, silicon ink7, photoelectric solar cells8, high power density batteries9, thermoelectrics10, light emitters11, seed crystals, and catalysts12. There are a wide variety of (generally expensive) ways to prepare silicon nanoparticles13. But such production methods typically have cost, shape, and/or product characteristic drawbacks. Accordingly, there is a need for inexpensive bulk manufacturing methods capable of producing nanosilicon powders with a broad range of product characteristics and uses.
There is also a need for energetic nanopowders, compositions and composites which are designed for specific uses with various characteristics including composition, structure size, shape, phase structure (eg, amorphous, multicrystalline or monocrystalline condition), reactant structure, surface/layer composition(s), grafting, purity, doping, and compatibility within composite compositions. Flakelike noncontinuous fluorocarbon coatings have been applied to relatively large silica particles by expensive plasma-enhanced chemical vapor deposition (PECVD) with a goal of being able to coat aluminum particles14. In attempts to limit progressive aluminum nanoparticle surface oxidation, coatings have also been applied to aluminum by perfluoroalkylcarboxylate reaction with surface Al—OH groups, leaving an intermediate oxygenated layer, and nickel coatings have been attempted to address the oxidative storage-instability of aluminum nanoparticles. AlB2 (perhaps as a coating on) aluminum nanoparticles formed by expensive electrical resistance explosion of aluminum/boron has been tested to protect against aluminum surface oxidation15. However, nanosilicon powders are inherently more storage-stable than aluminum nanoparticles. Accordingly, to realize and facilitate practical storage-stable and affordable propellant and explosives applications, new scalable methods and composition designs which facilitate storage stability and minimize oxide surface layer formation and oxidative aging are important for manufacture of inexpensive high energy nanosilicon powders which do not substantially degrade over time.
For some applications such as self-consuming munition casings, structural rocket fuel, and UAVs and other autonomous “disposable” or self-destructible military drones, structural energetics are needed which have physical strength in addition to high energetic output. Energetic composites reinforced with nanosilicon particles covalently bonded within a polymeric matrix could provide strong energetic materials. Energetic graphene could also reinforce energetic matrices. Graphene sheets are thin, one-atom-thick layers of sp2 hexagonal carbon atoms, which have extraordinary electronic and mechanical properties16. Graphene sheets have extreme stiffness and strength with nanoscale flexure-without-brittle-cracking capability, together with high thermal and electrical conductivity17. Preparation of a wide variety of pristine, derivatized, multilayer and/or partially-oxidized forms of graphene can be readily carried out18. Partially-oxidized graphene nanosheets have been tested as an additive19 to improve nitromethane decomposition, perhaps via thermal transfer and/or catalysis.
Graphene and precursor graphite are readily oxidized to introduce —COOH, ketone, oxirane and hydroxyl groups, over a very wide range of carbon-to-oxygen ratios20. Graphene oxide sheets may also be reduced back to sp2 sheet form at selectable lower levels of pendant oxygen-containing groups—in fact, graphene oxide can rapidly, even “explosively”, revert to more regular hexagonal sp2 graphene structures upon sufficiently intense light flash, providing a mechanism for simultaneous multi-location or patterned activation, reaction initiation or detonation21.
Graphene sheets are conventionally functionalized at their less-stable edges, including by preferential reaction with acidic —COOH and ketone/aldehyde groups which are typically present from a number of conventional processes used in their manufacture22. A common approach to graphene functionalization has been isocyanate reaction with carboxylic acid groups at graphene edges23. Reactions with surface hydroxyl and oxirane groups, and the sp2 carbon backbone also provide routes to functionalization with the graphene surface structure24.
There has been substantial work done on covalent grafting to graphene and graphene oxides. This work includes grafting of long alkyl chains by amidation reaction25, and covalent diazonium addition to graphene to initiate radical polymerization (eg, polymerization of styrene grafted to the graphene)26. If energetic groups such as nitrate —NO2, nitrate ester —O—NO2, and/or azide groups could be directly or indirectly (eg, by grafting of nitrate and/or azide-containing monomers or polymers) coupled to graphene sheets, important new energetic materials would be provided.
It is an object of the present invention to provide such processes for manufacturing silicon nanopowders, and new nanosilicon compositions. It is also an object to provide high performance energetics, and energetic applications, including composite energetics, munitions and propulsion systems which include nanoscale silicon as an energetic component.
These and other objects will be apparent from the following Summary, Figures, and Detailed Description of various embodiments of the present disclosure.